Researchers
Warn Chemicals Impair Brain Development
(Beyond Pesticides, November 14, 2006) Chemicals,
including pesticides, may be causing a "silent pandemic" of
brain diseases, researchers claim, impairing brain development, lowering
IQs and costing billions of dollars in lost productivity. Fetal and
early childhood exposures to industrial chemicals in the environment
can damage the developing brain and can lead to neurodevelopmental
disorders (NDDs)—autism, attention
deficit disorder, and mental retardation. Still, there has been
insufficient research done to identify the individual chemicals that
can cause injury to the developing brains of children.

In a new review
study, published online inThe
Lancet on November 8, 2006, researchers from the Harvard School
of Public Health and the Mount Sinai School of Medicine systematically
examined publicly available data on chemical toxicity in order to identify
the industrial chemicals that are the most likely to damage the developing
brain.

The researchers
found that 202 industrial chemicals have the capacity to damage the
human brain, and they conclude that chemical pollution may have harmed
the brains of millions of children worldwide. The authors further explain
that the toxic effects of industrial chemicals on children have generally
been overlooked.

To protect children
against industrial chemicals that can injure the developing brain, the
researchers urge a precautionary approach for chemical testing and control.
Such an approach is beginning to be applied in the European Union. It
puts in place strong regulations, which could later be relaxed, if the
hazard were less than anticipated, instead of current regulations that
require a high level of proof. At present in the U.S., requirements
for toxicity testing of chemicals are minimal.

The idea behind the Precautionary Principle is that in most cases, by
the time we have undeniable scientific proof of harm - the damage will
likely be too severe to correct. Therefore, the Principle is often referred
to as the "common sense approach." Advocates for environment
and human health promote the use of the Precautionary Principle due
to the broad recognition that there is often a considerable gap in our
knowledge of the impacts of chemicals once released in the environment.
By using the Precautionary Principal, organizations seek to prevent
chemical exposure and utilize known non-harmful, or least-toxic alternative
techniques and products.

“The human
brain is a precious and vulnerable organ. And because optimal brain
function depends on the integrity of the organ, even limited damage
may have serious consequences,” says Philippe Grandjean, M.D.,
Ph.D., adjunct professor at Harvard School of Public Health and the
study’s lead author.

One out of every six children has a developmental disability, usually
involving the nervous system. Treating NDDs is difficult and costly
to both families and society. In recent decades, a gathering amount
of evidence has linked industrial chemicals to NDDs. Lead, for example,
was the first chemical identified as having toxic effects to early brain
development, though its neurotoxicity to adults had been known for centuries.

A developing brain
is much more susceptible to the toxic effects of chemicals than an adult
brain. During development, the brain undergoes a highly complex series
of processes at different stages. An interference—for example,
from toxic substances—that disrupts those processes, can have
permanent consequences. That vulnerability lasts from fetal development
through infancy and childhood to adolescence. Research has shown that
environmental toxicants, such as lead or mercury, at low levels of exposure
can have subclinical effects—not clinically visible, but still
important adverse effects, such as decreases in intelligence or changes
in behavior.

Dr. Grandjean and
co-author Philip J. Landrigan, M.D.,
Professor at Mount Sinai School of Medicine, compiled a list of 202
environmental chemicals known to be toxic to the human brain, but note
that the list should not be regarded as comprehensive; for example,
the number of chemicals that can cause neurotoxicity in laboratory animal
tests exceeds 1,000. The authors then examined the published literature
on the only five substances on the list—lead, methylmercury, arsenic,
PCBs and toluene—that had sufficient documentation of toxicity
to the developing human brain in order to analyze how that toxicity
had been first recognized and how it led to control of exposure.

“Even if substantial
documentation on their toxicity is available, most chemicals are not
regulated to protect the developing brain,” says Dr. Grandjean.
“Only a few substances, such as lead and mercury, are controlled
with the purpose of protecting children. The 200 other chemicals that
are known to be toxic to the human brain are not regulated to prevent
adverse effects on the fetus or a small child.”

Dr. Grandjean and
Dr. Landrigan conclude that industrial chemicals are responsible for
what they call a silent pandemic that has caused impaired brain development
in millions of children worldwide. It is silent because the subclinical
effects of individual toxic chemicals are not apparent in available
health statistics. To point out the subclinical risk to large populations,
the authors note that virtually all children born in industrialized
countries between 1960 and 1980 were exposed to lead from petrol, which
may have reduced IQ scores above 130 (considered superior intelligence)
by more than half and increased the number of scores less than 70. Today,
it’s estimated that the economic costs of lead poisoning in U.S.
children are $43 billion annually; for methylmercury toxicity, $8.7
billion each year.

“Other harmful
consequences from lead exposure include shortened attention spans, slowed
motor coordination and heightened aggressiveness, which can lead to
problems in school and diminished economic productivity as an adult.
And the consequences of childhood neurotoxicant exposure later in life
may include increased risk of Parkinson’s disease and other neurogenerative
diseases,” says Dr. Landrigan.

The researchers
believe that the total impact of the pandemic is much greater than currently
recognized. In supplementary
documentation, about half of the 202 chemicals known to be toxic
to the brain are among the chemicals most commonly used.

Testing chemicals
for toxicity is a highly efficient public health measure. However, less
than half of the thousands of chemicals currently used in commerce have
been tested to assess acute toxicity and, although new chemicals undergo
more thorough testing, access to the data may be restricted because
companies fear exposing proprietary information. Also, current toxicity
testing rarely includes neurobehavioral functions.

“The brains
of our children are our most precious economic resource, and we haven’t
recognized how vulnerable they are,” says Dr. Grandjean. “We
must make protection of the young brain a paramount goal of public health
protection. You have only one chance to develop a brain.”